Investments in Partially Owned Entities (Summary of Condensed Combined Financial Information) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summarized financial information
Assets	$ 24,926,000	$ 25,526,000
Liabilities	21,357,000	21,162,000
Noncontrolling interests	265,000	146,000
Equity	3,305,000	4,218,000
Total revenue	13,600,000	13,423,000	$ 13,620,000
Equity in net income (loss)	$ (65,000)	$ (224,000)	$ (434,000)